Process for producing a fade-resistant paper

ABSTRACT

A process for producing a fade-resistant paper in which a cationic charged dye fixative is thoroughly mixed with fibers in a pulper, and a fade resistant pigment is added. To this mixture is added a three component retention system and the paper is formed on a Fourdrinier paper machine. After initial drying, the paper is treated with ethylated starch on a size press, and then finally dried.

BACKGROUND OF THE INVENTION

[0001] Currently, art rolls described as fade-resistant are marketed to schools. These rolls are treated by printing a pigmented color on one side of the sheet, with the other surface of the sheet remaining in the original color, usually white. These rolls are described as fading more slowly when exposed to sunlight as compared to conventional pigmented papers.

[0002] However, papers coated in this manner do not readily absorb marker ink, which tends to remain on the surface and smear, and it would therefore be advantageous to provide a paper in which marker ink is substantially absorbed.

SUMMARY OF THE INVENTION

[0003] It is therefore an object of the invention to provide a fade-resistant paper with color absorbed throughout.

[0004] It is a further object of the invention to provide a fade-resistant paper which readily absorbs inks placed on the surface thereof.

[0005] To achieve these and other objects, the invention is directed to a process for producing a fade-resistant paper comprising the steps of adding to fibers in a pulper a cationic charged dye fixative and thoroughly mixing, adding to the mixed fibers and fixative a fade resistant pigment, adding to the mixture of fibers, fixative and pigment a three component retention system, forming the paper on a Fourdrinier paper machine, initially drying the formed paper, treating the dried paper with ethylated starch on a size press, and finally drying the treated paper.

DETAILED DESCRIPTION OF THE INVENTION

[0006] According to the invention, a blend of softwood and hardwood pulp, typically in a ratio of 1:3-4 (softwood:hardwood) is added to a pulper to create a fiber slurry containing 4-12%, and preferably 5-7% solids, by weight. After about 5-10 minutes, the slurry is broken down into individual fibers, and a cationic dye fixative is added. While the preferred fixative is Intrafix GF from Sensient Corp., other similar cationic fixatives could be used. This positively charged fixative attaches itself to the negatively charged cellulose fibers in the slurry.

[0007] After the slurry is charged with the fixative and allowed to thoroughly mix over a period of 5-10 minutes, at least one fade resistant pigment is added in an amount of about 15 to about 400 lbs per ton of dry fiber. The amount of pigment added will depend on the depth and shade of color to be produced.

[0008] The amount of cationic dye fixative added will depend on the desired amount of pigment in the slurry. Thus, the amount of fixative will be about 15-25% by weight, preferably 20%, with respect to the amount of pigment to be added.

[0009] The pigmented pulp slurry is further treated in-line with three-component, colloidal silica-type filler retention technology to improve the amount of pigment retained during the process. This technology involves, first, the addition of a positively charged, cationic polymer to the pulp slurry to neutralize the normally negative charge that surrounds the small furnish fiber particles. By reducing the negative charge, the distance that separates the fibers is reduced and the particles come closer together. Complete neutralization is not required.

[0010] The preferred fixative is Nalkat 7607, a cross-linked, epichlorohydrin-dimethylamine (Epi-DMA) polymer sold by Nalco Chemical Company, Naperville, Ill. The range of usage is dependent on the charge of the system, but a typical range would be 0.2-1.5 lbs/ton of dry fiber and pigment.

[0011] A second component is then added, which is a long chain cationic flocculant, which spans the particles to form a

bridge

and causes the fiber to form flocs or agglomerates. This agglomeration improves fiber retention on the paper machine. The preferred flocculants are moderately charged, moderate molecular weight cationic emulsion flocculants. The preferred flocculant is Ondeo Nalco 01 PF067 sold by Nalco Chemical Company, Naperville, Ill., although other cationic polymer emulsions known in the papermaking art as flocculants, such as Ondeo Nalco 7520, are also acceptable. Range of usage is usually about 0.5-1.0 lbs/ton of dry fiber and pigment.

[0012] The final step is the addition of colloidal silica, which is added after the fiber flocs undergo a reduction is size caused by physical shear. Range of usage of the colloidal silica is 7-8.5 lbs/ton of dry fiber and pigment. This breakdown of the flocs allows them to release water and drain when the shear is complete. The small size of the colloidal silica then added results in formation of thousands of anionic sites that cause the smaller flocs to pull together when cationic patches exist on particle surfaces. The formation of these micro particles improves retention of the pigment.

[0013] The fiber/pigment slurry is then made into various basis weights of paper using conventional paper making equipment. The fiber slurry is distributed uniformly over a forming fabric. Water is removed by gravity and vacuum, and the wet pigment-colored web then undergoes conventional pressing and steam-heated drying to remove water. The dried sheet is treated with ethylated starch, and dried again to reduce the moisture content to 4-5%.

[0014] Comparative Test

[0015] A sample of paper produced according to the invention was placed in a

Fade-o-Meter

and exposed to a 2500 watt xenon bulb for 20 hours, together with a competitive sample, coated on one side only. The test was carried out in accordance with AATCC Test Method 16-1998 published by the American Association of Textile Chemists and Colorists. After 20 hours, equivalent to about 60-80 hours in direct sunlight, neither sample exhibited substantial fading. 

What is claimed is:
 1. A process for producing a fade-resistant paper comprising the steps of: adding to fibers and water in a pulper, a cationic charged dye fixative and thoroughly mixing; adding to the mixed fibers and fixative, at least one fade resistant pigment; adding to the mixture of fibers, fixative and pigment a three component retention system; forming the paper on a Fourdrinier paper machine, initially drying the formed paper; treating the initially dried paper with ethylated starch on a size press; and finally drying the treated paper.
 2. The process of claim 1, wherein the fibers added to the pulper comprise a blend of softwood and hardwood pulp in a ratio of 1:3-4 softwood:hardwood.
 3. The process of claim 1, wherein the fibers and water in the pulper form a slurry containing 4-12% by weight water.
 4. The process of claim 1, wherein the at least one pigment is added in an amount of 15 to 400 pounds per ton of dry fiber.
 5. The process of claim 1, wherein the addition of the three component retention system comprises the sequential addition of a positively charged cationic polymer to neutralize a normally negative charge on the fiber, a long chain cationic flocculant to increase floc size and colloidal silica to promote formation of micro particles. 